Relative identifiability of analog vs prime extraterrestrial signals

SETI's search for alien contact includes detecting intelligent analog transmissions and also those carrying sequences of prime numbers signifying life elsewhere in the Galaxy.

What is the relative ease with which SETI can discern rational analog vs prime number transmissions? Is it a waste of time to search for one over the other? There is no known natural source which generates prime numbers, and analog signals experience more interference from electromagnetic physical phenomena.

Would not the very quality of premeditated prime numbers as foriegn to naturally occuring electromagnetism create comparative difficulty in demodulating a given signal?